Abstract: In Western theories of international relations, realism is an important tradition. The relation between the theory of global justice and realism is an issue that political philosophers have to treat seriously. On the one hand, we should clarify that morality is relevant to international relations and criticize the strong version of realism in order to pave the way for the theory of global justice. On the other hand, we should notice that it is not morality but moralism that contemporary mainstream realism represented by Hans Morgenthau rejects. In this sense, the theory of global justice seems compatible with temperate versions of realism. They present two indispensable perspectives for the normative study of international relations.